Routine mammographic: screening has proven to be the only reliable diagnostic method for early detection of breast cancers. Current clinical mammographic imaging has been limited to a screen/film combination, but the advances in photodetector and direct x-ray converter technology has opened up the possibility of significantly improving mammographic screening with digital imagers. One limitation of some recently developed digital imagers is a limited optical fill factor in the photodetector. In this context, the optical fill factor is defined as the percentage of a pixel's area sensitive to visible light. State-of the-art active-matrix flat-panel imager (AMFPI) systems have optical fill factors ranging from 35%-60%. A small fill factor reduces the amount of light collected from individual x-ray interactions in the screen. It can also lead to an overall reduction in the number of x-ray quanta detected. A reduction in x-ray quanta corresponds to a fundamental reduction in detective quantum efficiency, and therefore a reduction in lesion detectability. One way to increase the number of detected x-ray quanta in digital imagers is to improve the fill factor of the photodetector array. However, with current technology, there is a minimum space requirement for the data and control lines between the pixels. This requirement causes the fill factor to decrease rapidly with decreasing pixel size. In this investigation, the applicants proposed a technique for improving the effective fill factor of any indirect detection imager by incorporating a focusing microlens array between the phosphor screen and the photodetector. With the ability of manufacturers to fabricate small diameter, large numerical aperture microlens arrays, the applicants hypothesized that this technique will allow the photodetector to detect all x-ray interaction events and, on the average, a larger number of light photons per x-ray interaction without significant image blurring. In addition, the size of the microlenses can be reduced to match the pixel sizes necessary for mammographic imaging. In this study, the applicants proposed to investigate and design microlens arrays that maximize the light collection efficiency and effective fill factor when combined with an AMFPI. The properties of this prototype imager will be measured, and the imaging performance compared to a system without the focusing microlenses. If the microlens array coupled AMFPI technology is successfully developed, it will speed the development of digital mammography detectors with pixel sizes smaller than 100 gm and their acceptance for clinical practice.